Onion is a cool-season vegetable that can be grown successfully throughout most of temperate North America. Onions may be grown from sets, transplants or seeds.
Onions start bulb formation when the day length is of the proper duration and different varieties of onions require different day lengths to initiate bulbing. In general, most common varieties fall into one of two classes, long-day (for northern latitudes) and short-day (for southern latitudes). For this reason, onion varieties that are grown in the South are not adaptable to the North and vice versa. Late plantings of the suggested varieties also result in small bulbs or lack of bulbing altogether in any location.
High temperatures and low humidity are advantageous during bulbing and curing. Onions have shallow roots and compete poorly with weeds and grasses. Timely shallow hoeing and cultivation are important, especially when the onions are small.
Onions may be eaten raw, broiled, boiled, baked, creamed, steamed, fried, french fried and pickled. They are used in soups and stews and combination with vegetables and meats.
Onions From Sets
Growing green onions from sets is probably the simplest method for the home gardener. The plants are quickly established and become vigorous and strong. Onion sets may be used to produce both green onions and dry onion bulbs, though production of really premium dry onions requires methods described in the following section.
Onions from Transplants
Transplanting young onion seedlings is the method of growing that most regularly produces large, dry, attractive onions for slicing (as shown in catalog pictures). Transplants are purchased in bundles (usually 60 to 80 plants) from garden stores and through seed and nursery catalogs (though mail-order onion plants often cost as much as buying the 60 to 80 full-size mature bulbs they may produce).
Several varieties are used for onion sets. All of these varieties are widely adaptable. The home gardener has little choice of varieties at the store, however, because sets are seldom sold under varietal names, merely by color: yellow, white or red. Yellow sets are sometimes sold as the varieties Ebenezer or Stuttgarter.
Purchase firm, dormant sets early - before they begin growth in heated salesrooms. Store sets in a cool, dry, dark environment if planting must be delayed after purchase. Divide the sets into two sizes before planting. Large sets (larger than a dime in diameter) are best used for green onions. If allowed to grow, these sets may "bolt" and form flower stalks. The small sets (smaller than a dime in diameter) produce the best bulbs for large, dry onions; and they usually do not "bolt." Extremely cold weather during early season growth also may condition onions from sets to flower.
Round onion sets produce flat onions; elongated or torpedo-shaped sets mature into round onions. Most gardeners prefer white sets for green onions, although red or yellow sets are also acceptable.Onions From Transplants
Gardeners should try to match varieties to their location. Long-day onions are bred for best performance in the North and short-day varieties perform best in southern locations. Short-day varieties may perform acceptably in the North if the plants can be set out very early in the season. Long-day types may not get the bulbing signal in the Deep South and so should be avoided there.
The normal garden center may offer Yellow and White Sweet Spanish (long-day varieties), Yellow and White Bermuda (short-day varieties and a red variety that may or may not be named (Southport Red Globe, perhaps; a long-day variety). Catalog shoppers may choose from a slightly wider variety selection, which may include Texas Grano (short- day), Vidalia Sweet (really a Granex hybrid, short-day), Red Hamburger (short-day), Walla Walla Sweet (long-day) and Texas 1015Y Supersweet (short-day). Prices normally are two to three times as high through catalog sales and may be as much as ten times as high. Only individual consumers can judge if this cost is justified for trying a new variety.
When To Plant
Sweet corn requires warm soil for germination (above 55°F for standard sweet corn varieties and about 65°F for supersweet varieties). Early plantings of standard sweet corn should be made at, or just before, the mean frost-free date unless you use special soil-warming protection such as clear polyethylene mulch film.
For a continuous supply of sweet corn throughout the summer, plant an early variety, a second early variety and a main-crop variety in the first planting. For example, you may wish to select Sundance (69 days) for the first early variety, Tuxedo (75 days) for the second early variety and Incredible (83 days) for the main-crop variety. Make a second planting and successive plantings of your favorite main-crop or late variety when three to four leaves have appeared on the seedlings in the previous planting. Plantings can be made as late as the first week of July.
Onions can be planted as soon as the garden can be tilled in the spring, usually late March or early April in prime regions for producing onions. Good fertility, adequate soil moisture and cool temperatures aid development.
Spacing & Depth
To produce green onions, plant the larger sets 1 _ inches deep and close enough to touch one another (green onions are harvested before crowding becomes a problem). To produce dry onions, plant the smaller sets 1 inch deep, with 2 to 4 inches between sets. Allow 12 to 18 inches between rows. If sets are 2 inches apart, harvest every other plant as green onions so that bulb development of the remaining sets is not impeded by neighboring plants.
Plant in fertile soil in early spring. Space the plants 4 to 5 inches apart in the row to produce large-sized bulbs (closer spacing significantly decreases bulb size) or space 2 to 2 _ inches apart and harvest every other plant as a green onion. Allow 12 to 18 inches between rows or space onions 6 to 8 inches apart in all directions in beds. Set the transplants 1 to 1 _ inches deep and apply 1 cup per plant of a starter-fertilizer solution.
Keep onions free from weeds by shallow cultivation and hoeing. To develop long, white stems for green onions, slightly hill the row by pulling the loose soil toward the onions with a hoe when the tops are 4 inches tall. Do not hill onions that are to be used as dry onions. Hilling may cause the necks of the stored bulb to rot.
Weeds and grass compete with the onion plants for nutrients and moisture during the growing season. Remove all weeds and grass by diligent and repeated shallow cultivation and hoeing. Side-dressing with fertilizer may be necessary.
Pull green onions anytime after the tops are 6 inches tall. Green onions become stronger in flavor with age and increasing size. They may be used for cooking when they are too strong to eat raw. Though leaves are traditionally discarded, all parts above the roots are edible.
Remove any plants that have formed flower stalks and use immediately. They do not produce good bulbs for dry storage. Harvest in late July or early August, when most of the tops have fallen over. Allow the plants to mature and the tops to fall over naturally. Breaking over the tops early interrupts growth, causing smaller bulbs that do not keep as well in storage.
Pull the mature onions in the morning and allow the bulbs to air dry in the garden until late afternoon. On especially hot, bright, sunny days, the bulb may sunburn. On days when this is likely, remove onions to a shaded location and allow them to dry thoroughly. Then, before evening dew falls, place them under dry shelter on elevated slats or screens or hang them in small bunches. Tops may be braided or tied with string before hanging. Full air circulation for 2 to 3 weeks is necessary for complete drying and curing. Keep the dry wrapper scales as intact as possible on the bulbs, as they enhance the keeping ability.
After the bulbs dry, cut the tops 1 _ to 2 inches long (at or above the narrow spot where the stem bent over), and place the bulb in dry storage with good air circulation. Do not try to store bulbs that are bruised, cut or diseased, or those with green tops or thick necks. Store under cool, dry conditions. Dry onions may keep until late winter, but check them regularly and use or discard those that begin to soften or rot.
Onions from Transplants
The earlier varieties are usually ready to harvest in July, with later varieties maturing into August. When most of the tops have fallen over, the onions may be pulled and dried (refer back to Harvesting under "Onions From Sets"). The length of storage time varies with the variety, with the sweeter varieties usually being the poorer keepers.
Above 40 degrees north latitude, root maggots may attack the roots of onion plants.